abstract statement of problem: bleaching systems with different concentrations and applications are widely used to improve the visual appearance of the teeth, but one of the complications of these materials is reduction of bond strength for immediately bonding to the bleached enamel. objectives: the aim of this study was to evaluate the influence of using different modified hydrogen peroxide bl...

In the crystal structure of the title molecular salt, 3C2H5N4(+)·HPO4(2-)·H2PO4(-)·3H2O, the phosphate-based framework is built upon layers parallel to (010) made up from the H2PO4(-) and HPO4(2-) anions and water mol-ecules, which are inter-connected through O-H⋯O hydrogen bonds. The organic cations are located between the phosphate-water layers and are connected to them via N-H⋯O hydrogen bon...

We propose a network rebonding model for light-induced metastability in amorphous silicon, involving bonding rearrangements of silicon and hydrogen atoms. Nonradiative recombination breaks weak silicon bonds and generates dangling bond-floating bond pairs, with very low activation energies. The transient floating bonds annihilate, generating local hydrogen motion. Charged defects are also found...

2,5,10,13-Tetraazatricyclo [12,2,2,26,9] icosa-1(16),6,8,14,17,19-hexene-3,4,11,12-tetraone tetraoxime (1a) and 2,5,11,14-tetraazatricyclo [13,3,1,16,10] icosa-1(19),6,8,10(20),15,17-hexaene-3,4,12,13-tetraonetetraoxime (1b) were obtained from condensation of 1,4- and 1,3-phenylendiamine with dichloroglyoxime, respectively. The reaction of 1,2-phenylendiamine with dich...

the solvatochromism of fluoresceine and its derivatives was studied in solvents of different hydrogen bond donor (hbd), hydrogen bond acceptor (hba), donor number (dn) and acceptor number (an) by their uv-vis spectra. results showed that position, intensity and shape of absorption bands change with type of solvent. these changes can be rationalized by solvatochromic parameters such as α, β, et ...

Computational studies are performed to analyze the physical properties of hydrogen bonds donated by Tyr16 and Asp103 to a series of substituted phenolate inhibitors bound in the active site of ketosteroid isomerase (KSI). As the solution pK(a) of the phenolate increases, these hydrogen bond distances decrease, the associated nuclear magnetic resonance (NMR) chemical shifts increase, and the fra...

The Front Cover shows an “O2 grasshopper” captured by two “Copper scorpions” using their strong claws and tails (outer-sphere hydrogen bonds). As the key intermediate in biological oxygenation, trans-1,2-peroxodicopper adduct was mimicked a variety of molecular copper complexes. structure-activity models hydrogen-bond-assisted tetradentate copper(I) chloride complexes were established, fundamen...

2,5,10,13-tetraazatricyclo [12,2,2,26,9] icosa-1(16),6,8,14,17,19-hexene-3,4,11,12-tetraone tetraoxime (1a) and 2,5,11,14-tetraazatricyclo [13,3,1,16,10] icosa-1(19),6,8,10(20),15,17-hexaene-3,4,12,13-tetraonetetraoxime (1b) were obtained from condensation of 1,4- and 1,3-phenylendiamine with dichloroglyoxime, respectively. the reaction of 1,2-phenylendiamine with dichloroglyoxime resulted in t...

Herein we describe a strategy for the preparation of artificial alpha-helices involving replacement of one of the main-chain hydrogen bonds with a covalent linkage. To mimic the C=O...H-N hydrogen bond as closely as possible, we envisioned a covalent bond of the type C=X-Y-N, where X and Y are two carbon atoms connected through an olefin metathesis reaction. Our results demonstrate that the rep...